Either you have witnessed a public display of affection and wish to creating hilarity for all by yelling this glorified phrase or you wish to add a supreme amount of emphasis to anything and everything.

The phrase must be said with over the top enthusiasm.

A straight back and forth motion of the arm is also encouraged in attempts to hyper enforce the phrase.

(Witnessing two uglies making out) "Woah, gross....GET SUM"(makes emphatic motion with arm until the uglies stop)

Frank: Watch me drink these beers
You: GET SUM

Sandra: I'm going for a job interview
Derek: You'll do fine, as long as you don't forget to GET SUM(makes motion with arm)

Guy one to Guy two: "Yo look Pete is pulling that hot blonde outta here"
Guy one and Guy two yelling from across the bar: "GET SUUUUUM"

The meaning of the phrase " Get sum " originates from the USMC in Vietnam. It was shouted loudly while fireing fully automatic machine guns to tell a superior officer that more ammo with be needed shortly.

Wrongly confused by most people to be a saying for some1 who is getting sex.